Corona from high voltage lines is a known problem and well established as a design criteria for high voltage electric power lines. Years ago a test known as the Radio Influence Voltage (RIV) test was implemented in response to corona interference causing AM radios in automobiles to become unusable while driving under and near power lines. Corona interference is known to become significantly worse in the presence of bad weather, such as rain and fog. The implementation of the RIV testing with associated electric power line design criteria helped improve the situation. When the original RIV approach was implemented there were no electric power sensors operating at high voltage, but the electric utility world has changed in that a variety of electric power sensors operating at high voltage are now readily available.
Avoiding corona when transmitting data along high voltage power lines can be facilitated by transmitting data at higher frequencies where the corona interference is less intense. While this may appear to be a good technical solution for many design objectives, the FCC only allows relatively low power levels to be transmitted in these unlicensed frequency channels. The combination of utilizing low power communications at these relatively high frequencies results in relatively shorter range data transmission capability, in some cases only a mile or two in dry weather and much less in heavy rain or fog. Reliable communications under these constraints therefore requires a large number of repeaters and specialized designs to focus the transmission of data packets directly between sources and receivers.
Another design concern arises with the placement of communication antennas. Electric power line data sensors, such as current transformers and voltage monitors, are ordinarily located in the high voltage field immediately next to the power line conductors, which also happens to be the location where the corona interference is most intense. Locating the antenna at high voltage within a corona field effectively de-tunes the antenna and changes its communication pattern degrading its ability to transmit and receive data. Corona interference created by power lines is also known to cause voltage spikes that can damage sensitive and expensive transmitter and receiver electronics. Providing the antennas with physical corona protection, such as shielding, generally makes antennas much larger and cumbersome. In addition, electronic filtering is largely impractical when the corona frequencies occur in the same range as the communication transmission frequency. As a result, there is a persistent need for a better solution for monitoring, communicating and responding to electric power line data.